1. Field of Invention
The present invention relates generally to luminaries for airfield lighting. In particular, the present invention relates to deployable elevated luminaries for portable airfield and heliport applications including omnidirectional runway edge lighting, threshold and stop bars, and unidirectional approach lights.
2. Discussion of Relevant Prior Art
The distinctive property of portable airfield lighting is the absence of power infrastructure on the site. There are currently two types of systems available for portable airfield lighting using conventional light sources. The first type of system includes a deployable version of airfield infrastructure having power generators, current regulators, cables, isolation transformers and luminaries. Unfortunately, this type of system is bulky, typically weighs in excess of 30,000 lbs, is packaged in six containers requiring 48 foot flatbed trailers for transportation, and requires a team of six people for installation that often takes over three hours.
The second type of portable airfield lighting system is based on the use of a rechargeable battery and a conventional filament bulb as a light source. Even though this type of system does not require the elaborate infrastructure associated with the first system, the luminaries are still heavy and bulky because they include two lead acid 12 v batteries. Additionally, the operation time on this second system without recharging is limited to 8-10 hours. Finally, high intensity approach lights cannot be operated from the battery but rather require the use of a generator.
What is needed, therefore, to overcome these limitations found in conventional systems is the application of solid-state technology (e.g., light emitting diodes) as a light source for portable airfield luminaries. Portable airfield luminaire using LEDs would utilitize low power consumption and the system would be significantly smaller and lightweight than conventional systems.
One of the requirements for airfield lighting systems including portable systems is related to the government (Federal Aviation Administration—FAA) and international (International Civil Aviation Organization—ICAO) specifications. These specifications identify light intensity in a variety of directions, color, dimensions and other design parameters. In particular, spatial light distribution in the horizontal plane varies from several degrees to omnidirectional (360°), while in the vertical plane it does not exceed 10° for the main beam.
The luminous intensity required for airfield lights varies from several candelas to in excess of 10,000 candelas, which makes implementing LEDs into portable airfield lighting systems extremely difficult. For example, in order to use LEDs in a system, the luminous flux generated by a single LED is still limited, thereby necessitating the combination of multiple LEDs. Additionally, the spatial light distribution emitted by the LED depends on the primary optics integrated into the LED package. Therefore, any previous attempts to integrate multiple LEDs into an airfield lighting system rely on a specific design of the primary optics. Unfortunately, practical implementation of a multiple LED system has not been realized because of this reliance on a specific primary optic design.
The majority of manufacturers have in production LED packages with the primary optic designed to provide a symmetrical pattern with low (6° to 15°), medium (15° to 45°) and wide (up to 120°) divergence because of the nature of the asymmetrical pattern emitted by the LED's die (chip). In general, a primary optic with low divergence has more losses (e.g., it is less efficient).